1. Field of the Invention
The invention relates generally to socket tools of the type used for socket wrenches and the like and, more particularly, to socket tools of the type which are designed for used in environments which are corrosive or present a spark or shock hazard.
2. Description of the Prior Art
Socket tools are typically formed of a suitable metal, such as steel, for strength and toughness. However, it is known to provide socket tools formed of a non-metallic material, such as a suitable plastic material, for use in applications which might present a corrosive environment or an electrical spark or shock hazard. It is also known to provide a metal insert in such a non-metallic socket tool for engagement with the associated driven member to improve the strength and/or wear resistance of the tool. In this regard, the present invention is an improvement of the composite socket tools disclosed in commonly owned copending U.S. application Ser. No. 698,782, filed Aug. 16, 1996 and entitled "Composite Socket with Double Inserts." That application discloses a socket tool body formed of a glass-fiber reinforced nylon material with insert molded metal inserts in both the driving and driven ends thereof. The inserts have knurls or serrations on their outer surfaces to inhibit rotation relative to the tool body.
In has been found that, under very high torque loads, such insert-molded socket tools may tend to fail by fragmenting apart. It is believed that this occurs by reason of fracture lines propagating along knurls on the outer surface of the insert and causing portions of the surrounding plastic material to break away.